1. Field of the Invention
This invention relates to control of the motor of a printer and, more particularly, to a motor control system of a printer of the type wherein printing of characters is performed while effecting slow-up over a space or interval between characters, which operates in such a manner that slow-up is effected even in a zone exceeding the space between characters and a print action is performed while slow-up is taking place.
2. Description of the Prior Art
As shown in FIG. 1, the printer comprises a platen 1, a carriage 3 for moving relatively a head 2, a carriage shaft 4 for supporting the carriage, and the combination for moving actually the carriage, composed of a transmission system 5, A-pulley 6, B-pulley 7, and stepping motor 8. Print action is performed in such a manner that a paper is colored by applying some print commands to the head 2 in synchronization with rotation of the stepping motor 8. As shown in FIG. 2, a printer drive circuit drives, by means of a microprocessor 9, the head 2 and stepping motor 8 by the use of a head driver 10 and motor driver 11. FIG. 3 is a drive timing chart showing a print action according to the prior art, of the head 2 and stepping motor 8, with showing the amount of head movement in correlation with the former. In this drawing, the abscissa indicates the time, and the ordinate indicates drive pulses applied to the head 2 and stepping motor 8 as well as the amount of movement of the carriage 3 when these pulses are applied.
In the conventional drive system, as represented by the curve A of FIG. 4, the drive frequency of the stepping motor 8 is slowed up from f.sub.1 to f.sub.2 by making use of steps corresponding to the number of characters, then, after the drive frequency required is attained, the stepping motor 8 is further driven at a constant speed, during which the print command is applied to the head 2 under the state of constant speed.
In the foregoing operation, by making use of the space between characters, slow-up is effected over that space.
It is desired to increase the print speed; however, according to the prior art, it is hardly possible to effect slow-up successfully thereby resulting in a desired high-speed state within the space between characters. That is, it is undesirable to try to attain a more high print speed than that attained in the prior art within the same number of steps as counted at the stepping timing of the stepping motor. The reason is that if the slow-up of the motor were effected rapidly, the movement of the carriage caused by rotation of the motor becomes not smooth, the quality of print is actually degraded, and there arises the phenomenon that characters are misaligned.